1. Field of the Invention
The present invention relates to a power steering system that transmits the steering torque applied by a driver to wheels via a steering transmission mechanism while allowing an electric motor to boost the steering torque. More specifically, the present invention relates to a power steering system provided with a collision detecting function of detecting the impact of a peripheral component on the steering transmission mechanism.
2. Description of the Related Art
A power steering system has been available that is characterized by including: a torque sensor for detecting the steering torque applied via a steering wheel of a vehicle; a motor that performs driving operation to assist steering according to the detection signal from the torque sensor; a motor driver circuit that drives the motor; a power-supply switching means for switching on and off the power supply to the motor driver circuit; and a control circuit that allows the power-supply switching means to supply power when the motor driver circuit is made active, and that controls the driving of the motor that is performed by the motor driver circuit, according to the magnitude of the steering torque detected by the torque sensor, wherein a shock detection means for detecting the shock provided to the vehicle is provided to determine, from the detection signal from the shock detection means, whether the shock is caused by the collision of the vehicle, by using the control circuit, and, if it is determined that the shock is caused by the collision, driving the motor is stopped, and the power-supply switching means is allowed to cut off the power supply. Such a power steering system is disclosed in Japanese Patent Application Publication No. 2000-72007, for example. When it is determined that an object collides with the vehicle from the detection signal from a collision detector for an air bag system, the power steering system stops driving the motor for an Electric Power Steering (EPS), thereby preventing an overcurrent from flowing through the motor driver circuit.
However, the conventional electric power steering system determines from the detection signal from the collision detector for an air bag system whether the collision with the vehicle has occurred. For this reason, there is a possibility that, although the collision of an object with the vehicle is detected, the impact on the EPS mechanism itself cannot be accurately detected. In addition, there is a problem that the impact of a peripheral component on the steering transmission mechanism cannot be surely detected because the shock detection means for detecting the shock provided to the vehicle is not the sensor that directly detects the acceleration of the steering transmission mechanism but an acceleration sensor to be used to determine whether a passive safety device, such as the air bag system, should be activated.